This invention relates to a process for encapsulating biologically active materials such as cells or tissues or biochemically or chemically active compositions and to the encapsulated system including the active materials.
In biochemical production and biotechnological applications, health and viability of active materials such as cells, microorganisms and the like, is important since these active materials are capable of producing biologically or biochemically active components that find a wide variety of use. For example, cells are capable of producing antibodies, hormones, lymphokines, antibiotics, interferons and other biochemicals or chemicals. Mammalian cell lines are grown by being surrounded by an aqueous medium containing a nutrient in order to promote the viability and growth of the cells and enables continued production of the desired microbiological or biological products. It has been proposed to utilize so-called microcarriers, which are beads having the appropriate charge and exchange capacity to promote the growth of the cells thereon in an efficient manner. The microcarriers themselves are maintained in an aqueous suspension containing the proper nutrient composition to promote cell growth and production of the desired microbiological product. Biological products which are shed or excreted from the cells become admixed with the aqueous suspending composition, which in many cases, is at very dilute concentrations. The subsequent recovery of the desired product is thereby rendered difficult and time consuming.
In order to overcome problems associated with microbiological product recovery, it has been proposed to encapsulate cells or microorganisms within a membrane which permits nutrients to be metabolized by the cell or microorganism while retaining the microbiological product produced by the cell or microorganism within the encapsulating membrane. Such processes are disclosed, for example, in U.S. Pat. Nos. 4,409,331 and 4,352,883. The semipermeable membrane surrounding the biologically-active material has a selected permeability so that substances having a certain molecular weight or below, are allowed to pass through the semi-permeable membrane. By controlling the permeability of the membrane, and by having a knowledge of the approximate molecular size of the desired product, one can confine the product, within the space between the active material and the semi-permeable membrane. Unfortunately, the process described in U.S. Pat. Nos. 4,409,331 and 4,352,883 require that the membrane be formed from the surface of an initially formed solid gel bead. This requires that the interior of the bead be subsequently liquefied so that the diffusion of nutrient which are required by the microorganism or cell, will not be hindered thereby to promote formation of the desired microbiological product. Furthermore, liquefication of the gel is highly desired so that the space between the semi-permeable membrane and the microorganism or cell is available for either cell production or products. Typically, these prior art membranes are formed from a cell suspension in alginate solution which is added dropwise to a calcium chloride aqueous solution, thereby to form solid gel beads. The beads then are washed with N-cyclohexylamine ethane sulfonic acid (CHES) and then washed subsequently with sodium chloride. Thereafter, a polylysine solution is added to form a polymer complex with a alginate surface. This surface then is washed with CHES/sodium chloride, subsequently with calcium chloride and then subsequently with sodium chloride. The membrane then is incubated and the gel within the membrane is subsequently liquefied by washing twice with sodium chloride, incubating, washing with sodium citrate and sodium chloride, washing with sodium chloride, and then a final wash. Obviously, such a process for forming encapsulated microbiologically active ingredients is time consuming and difficult and requires a high level of laboratory technique in order to successfully produce the encapsulated cell or microorganism suspended in a liquid medium. Furthermore, during these complicated time-consuming steps, the viability, productivity or other characteristic of the cell may be altered.
It would be highly desirable to provide a means for encapsulating a microorganism or cell capable of producing a biologically active material which eliminates the necessity of liquefying a solid carrier in order to promote mass transfer into and out of the cell or microorganism. Furthermore, it would be desirable to provide such an encapsulating means which is capable of drastically reducing the number of steps needed to form the encapsulated cell or microorganism. In addition, it would be desirable to produce such an encapsulating means which permits the formation of a membrane capable of having a permeability over a wide range, which permits the isolation of selective separation of a wide variety of biologically or chemically active molecules.